Aircraft comprise lift-generating surfaces to counter the force of gravity and sustain flight. In general, these lifting surfaces must have a sufficiently large planform area to produce adequate lift. Wings are the dominant lifting surface in most aircraft configurations. For a given wing planform area, a wing with a longer span tends to have increased efficiency at the expense of weight and storage footprint. As wing planform area and wing span increase, it becomes harder to store, transport, and otherwise accommodate aircraft on the ground, on a ship, and so forth.
To better and more compactly accommodate aircraft on the ground, wing folding systems have been developed. Many wing folding systems have been developed for naval fighter aircraft because of the unique requirements for stowage with a small footprint aboard an aircraft carrier or other ship. Most of these aircraft use one or more hinges on each side of the wing to fold or rotate a portion of the wing out of the nominal plane of the wing. Usually, the hinges on the left and right sides of the wing are parallel with the centerline of the aircraft for simplicity of engineering and manufacturing. Examples of this conventional approach include U.S. Pat. No. 2,290,850 to Umschweif, U.S. Pat. No. 2,623,713 to Foster, U.S. Pat. No. 2,712,421 to Naumann, U.S. Pat. No. 2,925,233 to Dunn et al., and more recently U.S. Pat. No. 5,381,986 to Smith. Of all the folding systems, parallel hinges are used on the largest number of operational aircraft, including for example the Boeing F/A-18E/F Super Hornet. Although most folding wing aircraft have wing tips that are quite far apart in the folded configuration, some folding-wing aircraft have wing tips that almost touch over the centerline when folded such as the Hawker Sea Hawk.
A few aircraft, such as the Douglas F4D Skyray, have fold lines that are not parallel to the aircraft centerline to avoid folding ailerons. However, for engineering and manufacturing simplicity, the left and right sides of the wing and fold system are symmetric about the centerplane of the aircraft. The wing tips also remain quite far apart in the folded configuration.
A few aircraft, such as the Fairey Gannet, have used a double fold system whereby the wing has two wing fold hinge assemblies per side, allowing the wing to fold twice for additional compactness. This adds additional weight and complexity to the aircraft. Still further, some aircraft, especially those designed to travel on roads as flying cars, incorporate one or more hinges that allow the wing to fold up and back out of the plane of the wing for compactness. Examples of this latter wing folding approach include U.S. Pat. No. 2,572,421 to Abel, U.S. Pat. No. 2,674,422 to Pellarini, U.S. Pat. No. 3,439,890 to Stits, and the Grumman F6F Hellcat and F4F-4 Wildcat.
Some wing stowage systems have been designed for missiles and munitions, which vary wing sweep without folding hinges to achieve compact stowage. Examples of such systems include U.S. Pat. No. 7,732,741 to Whitham, US D461159 to Mirales, et al, and the Small Diameter Bomb. For munitions, it is generally desirable to unfold the wings upon deployment. Some aircraft, such as the Bell/Boeing V-22 Osprey and U.S. Pat. No. 5,337,974 to Rumberger rotate the entire wing in the plane of the wing for compact stowage. Because these wings only rotate in plane, and do not fold out of plane, these are not considered wing folding systems.
Some other aircraft have variable wing sweep, including for example, the Grumman F-14 Tomcat, the General Dynamics F-111 Aardvark, and U.S. Pat. No. 4,569,493 to Burhans, et al. The predominant motivation for the variable sweep is to tailor performance to different flight speeds. As used herein, the term “wing folding system” does not encompass variable wing sweep systems that rotate wings in the plane of the wing during flight.
These and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
What all these prior art wing folding systems have in common is that they are symmetric systems, with symmetric wings and folding systems about the aircraft centerline, resulting a symmetric compact folded configuration. In particular, simple wing fold hinge lines parallel to the centerline are aerodynamically efficient, as they disturb only a small sliver of the airflow over the wing. Such symmetric designs also provide benefits in the form of common engineering processes and parts between left and right wings.
Even with the use of prior art wing folding systems, aircraft with especially long wing spans and high aspect ratios still have a large on-ground stowage footprint. Thus, there is still a need for a wing fold system that provides for increased compactness as compared with prior art systems.